” Since I have removed the roof brace to allow room for the water blocks and tubing, there is nothing under the feet in the lower cases to support the weight except for the strength of the sidewalls of the case themselves combined with the anti-flex strength of the top sheet of metal. This is a bad situation, and I have noticed minor bowing in the bottom case's top. A fourth PC would probably cause damage at best, and outright collapse at worst. These are not heavy duty cases ... imagine jumping on a cheapo case repeatedly, and you would see the reason that this may be a very bad situation if I continue my PC stacking without a supportive rack. “